Wireless communication systems, such as the 3rd Generation (3G) of mobile telephone standards and technology, are well known. An example of such 3G standards and technology is the Universal Mobile Telecommunications System (UMTS™), developed by the 3rd Generation Partnership Project (3GPP™) (www.3gpp.org).
The 3rd generation of wireless communications has generally been developed to support macro-cell mobile phone communications. Such macro cells are relatively large. They use high power base stations to communicate with wireless communication units within a relatively large geographical coverage area. These base stations are called ‘NodeBs’, in 3GPP terminology. One base station may provide coverage over several square kilometres.
Mobile and portable wireless communication units are often referred to as User Equipment (UEs), in 3G. The UEs communicate with a Core Network (CN) of the 3G wireless communication system. This communication is via a Radio Network Subsystem (RNS). A wireless communication system typically comprises a plurality of Radio Network Subsystems. Each Radio Network Subsystem comprises one or more cells, to which UEs may attach and thereby connect to the network. These cells may be termed ‘macro cells’. Each cell has one or more base stations within it, i.e. 3G NodeBs. The coverage area supported by each base station may be divided up into multiple sectors. Each sector may then be served by a dedicated antenna. The sectors typically lie in different directions from the base station.
Femtocells, picocells and “small cells” are a recent development within the field of wireless cellular communication systems. Femtocells, picocells and small cells are typically lower power cells, which have a smaller coverage area than macro cells. The term femtocell is also used hereafter to encompass picocells or small cells, or similar.
Femtocells are wireless communication coverage zones that cover a relatively small area of the cellular network, usually within or straddling the edge of a macrocell. Each femtocell is supported by a low power base station, which may also be referred to as a ‘Home NodeB’ (HNBs). A femtocell may support communications to UEs in a restricted area, for example within a building. Often, the coverage area of a femtocell lies entirely within one macro cell, and may lie entirely within one sector of the macrocell.
Typical applications for femtocells include residential and commercial situations, e.g. office locations, and communication ‘hotspots’ with high demand for communication links. In these uses, a Home NodeB can be connected to a core network of the communication system via, for example, the Internet. A broadband connection or the like may provide this connection. In this manner, femtocells can be provided in a simple, scalable deployment.
Femtocells may be a suitable solution for specific in-building locations where, for example, network congestion at the macro-cell level may be a problem. The majority of Home NodeBs are likely to be owned and deployed by members of the public, as opposed to a Network Operator owning a Node B. Predictions show that, globally, there will in future be many more femtocells than macrocells. In some locations in the US, there may already be five or more femtocells in the coverage footprint of any one macrocell.
One task that needs to be performed within communication networks is ‘Geo-location’ of UEs, which means determining where they are. If the location of the femtocell is known, then it may be used to help with geo-location. However, the location of the femtocell is often not known.
Table 1 below shows, in its left column, known techniques for locating femtocells. The right column of table 1 shows some limitations of those techniques.
TABLE 1Techniques for femtocell locationTechnique for locating femtocellLimitation or drawbackUse GPS chip-set built (i) Some femtocells don't have GPS;into femtocell(ii) Many femtocells are in urban locations or in buildings, and do not receive signals from enough GPS satellitesBilling recordsThe address on a billing record may relate to a completely different building than the one in which the femtocell is deployedUse location information for a Many UEs don't have an accurate way UE that is in communication of determining their location.with the femtocell.Information provided by a user/Data may not be provided at all, or mayproprietor of the femtocell, e.g. be inaccurate.input to website.Iteration of parameters, such (i) Time consuming;as latitude and longitude, and (ii) Has greater uncertainties and inspection of the consequences inaccuracies than algorithms that allow on ‘likelihood’ functionsfor direct solutions of latitude and longitude
In the remainder of this description, a mobile communications device such as a 3G ‘UE’ will be referred to as a ‘mobile communication unit’. The term ‘mobile communication unit’ also encompasses other mobile telephone, smartphone, or other wirelessly linked devices that are operable in a cellular wireless telecommunications network.
In a different field of technology, there are also known approaches to identifying or correcting the location of a base station, i.e. a NodeB. Patent Application WO2010/081659, assigned to Arieso, Ltd. and incorporated by reference herein in its entirety, provides a technique for refining data on base station locations. The approach in WO'659 involves creating probability density functions for the location of a mobile communication unit, based on communications with a mobile communication network. A confidence score may be calculated for each probability density function. A combined function can then be derived from the individual confidence scores. Maximisation of the combined function may then lead to a corrected value for the location of a base station.
In an asynchronous mobile communications network, the various macrocells and base stations do not operate with mutually synchronised time signals. Any two different base stations in such a network will tend to have time clocks that have different offsets, relative to any universal measure of time. Those offsets may themselves vary over time. An asynchronous network offers different challenges for geolocation of mobile communication units than synchronous networks, in which signals from different base stations are synchronised.
Patent Application WO2010/083943, which is also herein incorporated by reference, provides a method and system for locating wireless mobile communication units, in an asynchronous mobile communications network. As part of WO'943, a statistical approach is used to calculate the difference between timing offsets for pairs of base stations. This is achieved using the timing of signals received by one or more wireless communication units. In WO'943, having eliminated the variable timing offsets between pairs of base stations, geo-location techniques from synchronous networks may then be used to locate wireless mobile communication units in the asynchronous wireless communication system.
There is a need for an improved method and apparatus for locating a femtocell of a wireless communication network, whereby at least some of the above mentioned problems with known techniques are substantially alleviated. The challenges involved in locating femtocells differ from those involved in locating base stations or mobile communication units.